Low-temperature behavior of krypton monolayers on graphite

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Abstract
A calculation is performed for the low-temperature free energies of defect-free incommensurate monolayers of krypton on graphite. The calculation uses realistic potentials to describe the interactions between the atoms in the system, and takes into account the dynamic nature of the monolayer. The anharmonic nature of the interaction potential between adsorbed atoms causes the low-temperature behavior of the incommensurate monolayer to deviate from that predicted by harmonic calculations. The zero-point energy of the monolayer is significant, and reduces the critical value of the substrate corrugation to 7.0 K if the monolayer is to have a commensurate phase at low temperatures. Also, the zero-point energy cannot be neglected if the variation in the equilibrium misfit of the monolayer with chemical potential is to match that found by experiment. The (1/3 exponent of the misfit variation is found to be merely a consequence of the fact that the monolayer crosses over from having a domain-wall network to being weakly modulated over the range of misfit values considered by experiment. The value of the exponent is therefore not a universal value: Other similar systems may exhibit different exponents. The entropy contribution to the free energy is found to be small; the interactions between the domain walls, though weak, are sufficient to reduce the entropy of the domain-wall breathing mode. The free energy therefore does not vary significantly as the temperature of the system is increased from zero.